Surfboard safety fins with a rigid core and soft outer edges are disclosed in U.S. Pat. Nos. 5,273,472 and 5,941,347. The soft outer edges of these prior safety fins are generally a flexible edge border attached to the edge of a rigid fin core. The trailing and leading edges of the core have a raised ridge to provide a mount for the border. The edge border is molded to the core and over the ridge. The sides of the fin are the hard plastic exposed sides of the core.
A technique has been developed to encase the entire rigid core of a surfboard fin in a flexible material using plastic injection molding and to center the core in the mold cavity. Encasing the entire rigid fin core with a soft flexible material produces a safety fin. The entire core, including sides, is substantially covered by the soft flexible material. The flexible material can be extended to form borders around the leading and trailing edge of the fin core. The over molding technique creates a fin having a soft leading trail edge of a surfboard fin formed of a flexible material.
Fins with an over molded rigid core have been produced in the past using a method called “castable molding.” A rigid core is set into a mold filled with a soft flexible urethane material. The shape of the over mold determines the shape of the fin. The urethane cures after the fin core is inserted into the mold.
One of the problems with the castable molding method is keeping the core properly aligned in the urethane over mold. The standard alignment method is to clamp the base of the fin core in a device above the mold. If the fin core is not aligned properly or is not held in its correct position during the curing process of the over mold material, the fin core will be offset in the over mold. The resulting fin will not be useable for surfing. Another problem with castable molding is the slow curing time of the urethane. This problem extends the production time and increasing the costs of the fins. In view of these problems, over molded fins are no longer generally sold in the market place and were a commercial failure.
A faster and more cost effective method of over molding a core involves injection molding a soft material over a core. The core is clamped at its base, and is suspended or cantilevered inside the over mold cavity. The plastic material is injected into the cavity to over mold the entire core and fill the cavity.
The core alignment problem still exists with injection molding method. The pressure of the injected material into the fin cavity can bend or shift the suspended fin core in the mold cavity. Keeping a rigid fin core properly aligned in a mold cavity during the injection process is difficult. Failing to maintain proper alignment of the core in the mold may result in a high molded fin rejection rate. Accordingly, a method and apparatus is needed to align a fin core in an over mold so as to form a soft layer of safety fin.